title: Role of Host Sensitivity to Ptr ToxA in Development of Tan Spot of Wheat.
abstract: ABSTRACT Pyrenophora tritici-repentis race 2 produces Ptr ToxA, a host-selective toxin previously described as a pathogenicity factor for tan spot on wheat. The objective of this research was to evaluate the role of host sensitivity to toxin, conditioned by a single dominant gene on chromosome 5BL, in the disease development by race 2. An F(2)-derived F(6) recombinant inbred population of 108 wheat lines, produced from crosses of toxin-sensitive, disease-susceptible cv. Kulm with the toxin-insensitive, disease-resistant cv. Erik segregated 1:1 for toxin reaction. However, the population was skewed toward resistance to race 2 of the fungus. Toxin reaction accounted for 24.4% of the genetic variance for disease. Heritability estimates suggested the presence of four to five genes that influence disease reaction in the population. Toxin-insensitive mutants, previously derived Kulm, were susceptible to race 2, although disease developed more slowly on the mutants than it did on the wild-type Kulm. The data indicate that sensitivity to Ptr ToxA influences disease severity in some host genotypes without defining susceptibility.
authors.forename: T L
authors.initials: TL
authors.lastname: Friesen
authors.forename: S
authors.initials: S
authors.lastname: Ali
authors.forename: S
authors.initials: S
authors.lastname: Kianian
authors.forename: L J
authors.initials: LJ
authors.lastname: Francl
authors.forename: J B
authors.initials: JB
authors.lastname: Rasmussen